The United Stated patent of Anderson U.S. Pat. No. 4,080,699, which is assigned to the assignee of the present invention, discloses apparatus and a method for burnishing gears by a pair of spaced gear racks having toothed faces that oppose each other so as to mesh with a toothed gear therebetween during driven rack movement. Meshing of the rack and gear teeth provides the sole rotational support for the gear during the rack movement as the harder rack teeth concomitantly burnish the softer gear teeth. Very good results are achieved in performing the burnishing operation by virtue of the manner in which the meshing rack and gear teeth provide the rotational support for the gear during the burnishing. It is believed that the superior results are achieved due to the freedom of the axis of gear rotation to move with respect to the racks as the rack teeth engage defects on the gear teeth.
U.S. Pat. No. 4,208,773, which is also assigned to the assignee of the present invention, discloses a toothed burnishing rack that is capable of burnishing toothed gears such that each burnished gear tooth has accentuated axial crowns intermediate the axial ends of the tooth. The axial crowns are in the range of about four to seven ten-thousandths of an inch or greater in order to enhance gear performance and durability while doing so without excessively increasing the cost of the gear. To provide the axial crowns, the burnishing rack includes a toothed forming face having leading and trailing sections with one of the sections, preferably the trailing section, slightly inclined with respect to the other section in a lateral direction along the elongated length of the rack. In the preferred embodiment disclosed, the inclination of the one section of the toothed face with respect to the other section thereof is provided by making the rack in separate pieces and grinding a mounting surface on one piece to a slight inclination in a lateral direction along the length thereof with respect to its oppositely facing toothed face section. Mounting of the two pieces on a flat base positions the toothed face section on the one ground piece in a slight inclination with respect to the toothed face section of the other piece. Two such racks cooperate with each other to burnish gear teeth in the manner described above.